Copper(II)-catalyzed ether synthesis from aliphatic alcohols and potassium organotrifluoroborate salts

[reaction: see text] A protocol for the copper(II)-catalyzed etherification of aliphatic alcohols under mild and essentially neutral conditions is described. Air- and moisture-stable potassium alkenyl- and aryltrifluoroborate salts undergo cross-coupling with a variety of aliphatic primary and secondary alcohols and phenols, and are tolerant of a range of functional groups. The optimized conditions utilize catalytic copper(II) acetate with 4-(dimethylamino)pyridine as ligand in the presence of 4 A molecular sieves under an atmosphere of oxygen.     

Low-dimensional Compounds Containing Cyano Groups. XIII. Structural–spectral Correlation of Copper Dicyanoargentates

The new mixed-valence mixed-metal complex Cu(py)₆Cu₂Ag₂(CN)₆ (py = pyridine) possesses a three dimensional polymeric crystal structure. The Cu(I) atom is tetrahedrally coordinated by two nitrogen atoms of pyridine molecules, by one nitrogen atom of the dicyanoargentate anion and by one carbon atom of the cyano group. Both the dicyanoargentate anion and the cyano group bridge the Cu(I) atom with neighboring Cu(II) atoms. These are hexacoordinated in the form of an elongated tetragonal bipyramid. The equatorial plane is formed by two nitrogen atoms from two pyridine molecules and two nitrogen atoms from bridging cyano groups. Axial positions are occupied by nitrogen atoms of the bridging [Ag(CN₂]⁻ anions. Correlation between structures of the title compound and seven other dicyanoargentates with their i.r. spectra has been studied. The coordination mode of [Ag(CN₂]⁻ anions in compounds Cu_8-xAg_x(tn)₃(CN)₁₀ x = 0.25, Cu(3-Mepy)₂Ag₂(CN)₄, Cu(py)₂Ag₂(CN)₄ and Cu(py)₄Ag₂(CN)₄ (tn is 1,3-diaminopropane, 3-Mepy is 3-methylpyridine) is predicted based on this correlation.     

Ring-opening carbonyl–olefin metathesis of norbornenes

A computational and experimental study of the hydrazine-catalyzed ring-opening carbonyl–olefin metathesis of norbornenes is described. Detailed theoretical investigation of the energetic landscape for the full reaction pathway with six different hydrazines revealed several crucial aspects for the design of next-generation hydrazine catalysts. This study indicated that a [2.2.2]-bicyclic hydrazine should offer substantially increased reactivity versus the previously reported [2.2.1]-hydrazine due to a lowered activation barrier for the rate-determining cycloreversion step, a prediction which was verified experimentally. Optimized conditions for both cycloaddition and cycloreversion steps were identified, and a brief substrate scope study for each was conducted. A complication for catalysis was found to be the slow hydrolysis of the ring-opened hydrazonium intermediates, which were shown to suffer from a competitive and irreversible cycloaddition with a second equivalent of norbornene. This problem was overcome by the strategic incorporation of a bridgehead methyl group on the norbornene ring, leading to the first demonstrated catalytic carbonyl–olefin metathesis of norbornene rings.

A computational and experimental study has uncovered a second generation hydrazine that enables the catalytic ring-opening carbonyl–olefin metathesis of norbornenes.     

Solutions of logarithmic type for elliptic and hypoelliptic equations

LetK be an algebraically closed field withp:=char (K)>0 andX a bielliptic curve over Spec(K) with genus≥6 and such that the canonical model ofX is ordinary. In this paper we determine all the possible gap sequences of Weierstrass points on such curves.     

Processes associated with ionic current rectification at a 2D-titanate nanosheet deposit on a microhole poly(ethylene terephthalate) substrate

Films of titanate nanosheets (approx. 1.8-nm layer thickness and 200-nm size) having a lamellar structure can form electrolyte-filled semi-permeable channels containing tetrabutylammonium cations. By evaporation of a colloidal solution, persistent deposits are readily formed with approx. 10-μm thickness on a 6-μm-thick poly(ethylene-terephthalate) (PET) substrate with a 20-μm diameter microhole. When immersed in aqueous solution, the titanate nanosheets exhibit a p.z.c. of − 37 mV, consistent with the formation of a cation conducting (semi-permeable) deposit. With a sufficiently low ionic strength in the aqueous electrolyte, ionic current rectification is observed (cationic diode behaviour). Currents can be dissected into (i) electrolyte cation transport, (ii) electrolyte anion transport and (iii) water heterolysis causing additional proton transport. For all types of electrolyte cations, a water heterolysis mechanism is observed. For Ca²⁺ and Mg²⁺ions, water heterolysis causes ion current blocking, presumably due to localised hydroxide-induced precipitation processes. Aqueous NBu₄⁺ is shown to ‘invert’ the diode effect (from cationic to anionic diode). Potential for applications in desalination and/or ion sensing are discussed.

     

Head-to-head vinyl polymers. V. Preparation and characterization of alternating head-to-head copolymers of alkyl acrylates with alkyl methacrylates

Alternating head-to-head (h-h) copolymers of methyl or n-butyl acrylates with the corresponding methacrylates were synthesized by alternating copolymerization of ethylene with citraconic anhydride, followed by esterification and Characterization. The respective equimolar (1:) head-to-tail (h-t) copolymers were also prepared by conventional radical copolymerization as comparison. The alternating, relatively low molecular weight h-h copolymers obtained showed softening, glass transition, and degradation temperatures somewhat higher than those displayed by the 1:1 h-t copolymers. After pyrolysis the main decomposition products from both h-h and h-t copolymers were alcohols, acrylates, and methacrylates. Furthermore, the ratios of alcohols to acrylates were larger for the h-h than for the h-t copolymers and smaller for the methyl than for the n-butyl esters.     

Generating Function of the Tilings of an Aztec Rectangle with Holes

We consider a generating function of the domino tilings of an Aztec rectangle with several unit squares removed from the boundary. Our generating function involves two statistics: the rank of the tiling and half number of vertical dominoes as in the Aztec diamond theorem by Elkies, Kuperberg, Larsen and Propp. In addition, our work deduces a combinatorial explanation for an interesting connection between the number of lozenge tilings of a semihexagon and the number of domino tilings of an Aztec rectangle.     

Synthesis of benzannulated spiroacetals using chiral gold–phosphine complexes and chiral anions

The development of an asymmetric gold-catalysed dihydroalkoxylation strategy for the synthesis of the 3′H-spiro[chroman-2,1′-isobenzofuran] spiroacetal ring system 5 is described. Spiroacetal was generated in up to 87:13 enantiomeric ratio using chiral gold–phosphine complexes and chiral silver phosphate Ag(S)-TRIP.     

Synthesis and Evaluation of Chalcone Derivatives as Novel Sunscreen Agent

Ultraviolet (UV) irradiation is a serious problem for skin health thus the interest in the research to develop sunscreen agent has been increasing. Chalcone is a promising compound to be developed as its chromophore absorbs in the UV region. Therefore, in the present work, we synthesized eight chalcone derivatives through Claisen–Schmidt condensation at room temperature. The evaluation of the optical properties of each chalcone derivatives in the UV region was conducted through spectroscopic and computational studies. The synthesized chalcones were obtained in good yields and they were active in the UV region. The results revealed that more methoxy substituents to chalcone leads toward red shift. All chalcone derivatives have high molar absorptivity value (21,000–56,000) demonstrating that they have the potential to be used as the sunscreen agent. The cytotoxicity assay showed that chalcone derivatives were demonstrating low toxicity toward normal human fibroblast cell, which is remarkable. Therefore, we concluded that the synthesized chalcones in this work were potential to be developed as novel sunscreen agents in real application.     

Electronic structures of NbGen−/0/+ (n = 1–3) clusters from multiconfigurational CASPT2 and density matrix renormalization group-CASPT2 calculations

Density functional theory and multiconfigurational CASPT2 and density matrix renormalization group DMRG-CASPT2 have been employed to study the low-lying states of NbGe_n^−/0/+ (n = 1–3) clusters. With the DMRG-CASPT2 method, the active spaces are extended to a size of 20 orbitals. For most of the states, the CASPT2 relative energies are comparable with the DMRG-CASPT2 results. The leading configuration, bond distances, vibrational frequencies, and relative energies of the low-lying states of these clusters were calculated. The ground states of these clusters were computed to be ³Δ, ⁴Φ, and ⁵Φ of NbGe^−/0/+; ³A₂, ⁴B₁, and ³B₁ of cyclic-NbGe₂^−/0/+; and ¹A′, 1²A″ and 1²A′′ (²E), and ³A″ of tetrahedral-NbGe₃^−/0/+ isomers. For NbGe cluster, our calculations proposed that the ⁶∑ is almost degenerate with the ⁴Φ with the CASPT2 and DMRG-CASPT2 relative energies of 0.05 and 0.06 eV. The adiabatic detachment energies of NbGe_n⁻ (n = 1–3) clusters were estimated to be 1.46, 1.55, and 2.18 eV by the CASPT2 method. The relevant detachment energies of the anionic ground state and the ionization energies of the neutral ground states are evaluated at the CASPT2 level.